Electronic pointing devices sometimes transmit acoustic signals, and most often ultrasound signals, from which the position of the electronic pointing devices position may be determined. For example, a digital pen or stylus operates as a standard pen permitting the user to write on paper while transmitting pre-defined, encoded, ultrasound data that is received by a receiver and used to determine the position of the digital pen. The ultrasound data is sampled and decoded by the receiver, which may be mobile device, such as a smartphone, notebook, tablet PC, Slate, e-Reader, etc. Based on signal processing algorithms, the mobile device can determine the precise location of the pointing device and thus, the digital pen may serve as a data input apparatus for the mobile device. Ultrasound-based digital pens may be used as touch screen replacement/complement, high resolution graphical input device, navigation mouse, 2D/3D gaming, etc. Ultrasound technology, in general, may also be used to enhance user experience in applications such as hand gesture detection, finger hovering, and peer-to-peer positioning and communications.
The audio digitizers (CODECs) in the mobile devices that are used with ultrasound technology are typically part of the audio sub-system, which traditionally was used to sample and reproduce voice and music—all in the hearing range of frequencies (up to 25 kHz). The CODECs of traditional audio systems use a sampling frequency of up to 48 kHz. Recently, due to the emergence of various ultrasound technologies, CODECs are often designed now to support a higher sampling rate, e.g., up to 200 kHz and more, and thus are capable of sampling the ultrasound data transmitted by an ultrasound-based devices. The sampling rate, however, has a direct relation to power consumption, and thus the use of a higher sampling rate for ultrasound data results in increased power consumption. Moreover, processing of the ultrasound samples also contributes to CPU utilization, and as a result, consumes more power.